Drying materials



J. P. DEVlNE DRYING MATERIALS Filed May 28', 1927 2 Sheets-Sheet July 24, 1928 1,678,559

J. P. DEVINE DRYING MATERIALS Patented July 24,1928.

UNITED STATES JosErn: P. DEVINE, or BUFFALO, new You.

DRYING MATERIALS.

continuation of applitation Serial No. 124,317, filed July 23, 1826. This -Seri a1 No. 1s5,oss;

My invention relates to a method and apparatus for drying materials and has particularly in view the drying of porous materials. My method is of general application,

5 and can be utilized in connection with the drying of a. wide range of organic and inorganic materials, including high tension cables, telephone cables, wood, meat, hides, ceramics, plaster board, earthenware, brim quettes, paper, foundry molds and cores, tobacco,'mica sheets and other similar materials. 'While having its-present widest application in connection with the removal of the water-from -such materials, any other vaporizable material can be equally well removed, such'as, the various solvents that are used in manufacturing processes.

I will now describe my process and apparatus, and by way of example, in connection with the drying of wood, it being understood that other materials can be dried by the same type'of apparatus and in a similar manner.

Wood, after it has been sawed, is stacked and left;exposed to the air for a period of several weeks or months. This is usually referred to as air seasoning, and wood having been so seasoned usually retains a large 4 percentage of moisture. In order to be used for yarious purposes, the wood should contain a very small percentage of moisture, and

""to' remove the retained moisture the wood is furtherdried in kilns, the time varying from days to months. depending upon the character and dimensions of the wood, its moisture 35. content and the type of kiln employed. These dry kilns 0 rate in various ways, and am aware it h ss been proposed to dry woodin kilns by heating the-surrounding airand circulatinv it around thewood to 40 1 remove the excess moisture. I

Steam has also been similarly used fo the same purpose. Wood has also been dried ina vacuum with and-without the simultaneous action of heat.- -In all of these processes, however, the wood dries more rapidly on the outside than in the interior, with the result that the shrinkage is" not uniform,

and thus stresses result which may cause what is known iinthe artas checking case- Y g0 hardening, honeycombing and warping, and

rendering the wood unfit formany purposes. My process, however, is directed to the dryingof wood and other materials containing water or other vaporizabl-e substance, by

5 means of pressure reduced .below atmosjhardening, honeycombing application flled'lt ay 28, 1927.

pheric pressure,'herei nafter called reduced pressure and surrounded by saturated vapors. By constantly supplying and maintaining a. vapor surrounding the material being dried, I prevent the material near the surface from drying out first, as has heretofore been the case, and keep the moisture content of the material near the surface of the wood substantially as high or higher than the interior portion of the wood.

By carrying on my'dryingoperation under reduced pressurejl also reduce the temperature for drying, farbelow that which is ordinarily employed in thedrying of wood or other materials, and by vaporizing water or solvent, other than is contained in the materiaLbeing dried, at an extremely low temperature, I provide acarrying medium for the heat units, and thereby shorten the time of drying, and do not depend upon ra- 75 diation or induction-for transferring the heat in an apparatus operating under reduced ressure.

As t e water or solvent vaporizes within the vacuum chamber, the vapors preheatand in their passage through the vacuum apparatus come in contact with-the material be ing dried. q As the tem e'rature of the vapors at this oint exceed tl ie temperature of the wood, t ey condense on the surface of the wood which takes up the heat uni-ts. When tile vapor pressure on the inside of the wood equals or exceeds the'vapor tension on the outside, the moisture commences to leave the wood in the form of vapor from the inside out, with the result that the outside of the wood is in a moistcondition, until the last percentage of moisure is removed from the outer surface, facilitatingthe drying of the wood and preventingchecking, caseand warping. Referring to the drawings for a more completedisclosure' of the invention:

Fig. -1 is a longitudinal section of a vacuum dryer-. k M,

Fig. 2 isa transverse section of. Fig. 1. Fig. 3 is an elevation of an assembly of a vacuum dryer with a barometric condenser and vacuum pump.

-F'gs. 4: and 5 are elevations of an assem-' bly of a vacuum dryer with a surface condenser and vacuum pump. 7

The drying retort 1 isformed into a cylindrical or other conventional shape, and'can.

be made of boiler plate or other materials, 1

and has a door 2 at one or both ends pivotally mounted and supported from the arm 3 or can be hinged or operated by many well for supporting .the material. to be dried,

tracks 7 and 8 being'supported by the bottom of the retort, and on which the platform may slide in and out.

Running lengthwise and on the insideiof the. retort are heating elements, comprising separate groups of steam pipes 9, 10, 11 and 12, independently controlled and which serve to heat the contents of the retort and also aid by their location to offset any loss of heat by radiation through the walls of the retort. The eifect can be carried out by other mean, such as a steam jacket or jackets.

The subdivided heating elements have another advantage in permitting various steam pressures to be ,carried on the different groups of coils in order to maintain an even temperature throughout the apparatus.

In the bottom of the retort is a receptacle or vaporizer 13 provided with a supply pipe 14 for feeding water or other volatile'solvent thereto as desired, and a drain pipe 14 for drawing oli the water as'desiredQ Located adjacent to the receptacle 13 and in the bottom of the retort are coils of pipes 15 and 16 for supplying heat to the contents of the retort, and particularly to the vaporizing receptacle for causing evaporation of the water or solvent vapors therefrom.

The coils 15 and 16 in the bottom of the retort serve two purposes. It is very 'diihcult to transmit heat inside of a vacuum apparatus, particularly under .reduced presure. The location ofthe cluster of coils in the bottom of the retort is most efficient, since the heat from these coils rises, comes in contact with the wood, gives ofi" heat units to the wood and consequently facilitates evaporation or-drying. They also serve to evaporate the liquid in the vaporizer. It is apparent, however, that other positions of the coils and vaporizer might be employed than that shown and that other means than coils or a vaporizer could be used as a source of heat.

Extending lengthwise of the retort is a perforated steam spray pipe 17.

Surmounting the retort is a steam dome 18,-and'this may beconnected through the medium of a vapor pipe 19 to a conventional barometric condenser 20, provided with an air line separator 21, and tail pipes 22 and'23'leading to a hot well 24, to receive the condensate. f Any type of condenser may be employed.

Connected to the condenser by a suitable pipe line 25 is a vacuum pump 26. It will be. clear therefore that when the vacuum bination with the retort, a surface condenser Y 27, a receiver 28 for saving the condensate,

and a dry vacuum pump 29. A pressure gauge 3O 13 provided to indicate the amount of vacuum or reduced pressure within the retort, and a valve 31 is also provided to break the vacuum.

Operation.

The wood or other material to be dried is placed in the retort and the door or doors clamped tight. Steam is now admitted to the heating elements 9, 10, 1.1, 12, 15 and.

16, and low pressure steam may be injected into the interior of the retort through the perforated steam spray pipe 17, all for the purpose of preliminarily and rapidly" heatlng up the wood in the retort, care being "taken not to subject the wood to an injuriouslyhigh temperature.

Water having been already admitted to the receptacle or vaporizer, and heated up, the steam is now shutoff from the pipe 17, the. vacuum pump is started, the pressure reduced, and this condition maintained for a number of hours depending upon the particular kind of wood or other materials being dried. I

Assuming the wood to be first uniformly heated to a temperature less than the boiling point of water at atmospheric pressure, the obtainin and maintaining of a vacuum-will reduce t e boiling point of the water contained inthegwood as well as that in the vaporizer. This will, of course, cause rapid vaporization ofthe water, and as the vapor is evolved it will be drawn out of the retort by the vacuum pump. As the water in the wood vaporizes, it takes up its latent heat of vaporization from the wood. Thiscauses the wood to dro to a lower, temperature than the surroun ing saturated vapor with the result that the vapors in the retort will condense on the surface of the wood, imparting to the wood their heat units of condensation. By reason of the continuous vaporization of the water in the vaporizer, there is a continuous suppl of heat units to the wood, oflsetting thereby the tendency of the wood to drop to a lower temperature from the volatilizing of the water within its pores. It will be clear that so long as there is water in the vaporizer, which is in communication with the vapor in the interior of the retort, the vapor will remain saturated so long as an adequate supply of heat units are transmitted to the vaporizer. It is clear'too that so long as the wood is surrounded by saturated vapor no part of the woodcan become any drier than the vapor end in-view, the wood has first been driedsurrounding it. i This condition prevents causing uneven streses in the wood, checking, case-hardening, honeycombing and warping. Prior processes of drying wood have lar ely depended upon the estb-alishment and maintenance of a moisture gradicut to efiect the desired result. With that on the outside so that the moisture will flow from the inside to the outside. The effect of drying the wood on'the outside, however,

has been to close the pores of the wood there-- by-hindering the escape of vapor from the inside and causing stresses in thewood, with resulting checking and warping, case-hardening and honeycombing. In my process however, there is no uneven drying, the idea being to uniformly reduce the moisture content ofthe wood by exhausting the formed vapors, the presence of the saturated surrounding vapor acting as a control to prevent uneven drying of any portion. of the .wood. j

After all of the water in the wood has been evaporated, then there remains so much moisture as is contained in the saturated vapor corresponding to the pressure in the 1Ti5l2()1?l3. 1

With a vacuum maintained as high as 29", the total amountof liquid in the saturated vapor medium surrounding the wood will be very small. During the drying operation, the temperature ofthe wood will vary from approximately 160 F. with a 20" vacuum, and a total vapor pressure ofjabout -5 lbs. per square inch, to 60 to 80 F. with approximately a 29" vacuum and a total vapor pressure of approximately 0.5 lbs. per square inch.

Maple shoe lasts have been dried by my process to substantially bone dryness in 68 hours, and to commercial dryness inabout hours. The best that could bedone with current known processes was to.90 days.

While it may not be necessar to have the vapors entirely saturated as from vapors of relatively high humidity, still it is an advantage to have only saturated vapors, and in the embodiment of my process herein disclosed, I employ, only saturated vapors. Inasmuch as the water is vaporized inside the retort, the boiling point of that water is determined by the reduced pressure. under which the apparatus is operating. By creating the vapors inside the retort, they serve-not only as the heat carrying medium to the materials being -dried,'but also K Itwill be apparent therefore that while I have idescnbed my process in connection prevent harmful stresses occurring in the outer portion of the materials.

Thisapplication is a. continuation of my application Serial No. 124,317 filed July 23, 1926.

ifierentiated materials can be dried equally well wherever the same problem is presented. Such materials will include those where the pores of the material, contain the liquid which it is desired to eliminate, and wherein other drying methods would cause the outside portions to become dry before the interior.

I am' aware that my invention may be embodied in' other specific forms without de arting from the spirit or essential attri utesthereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive, reference being bad to; the appended claims, rather than to the foregoing description to indicate the scope of the invention.

, Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of d ing materials in a closed receptacle by sub ecting them to heat under a sustained reduced pressure during the entire drying operation in the presence of a vapor maintained at a relatively high humidity for an extended period of time and removing vapor from the receptacle during the drying operation.

2. Themethod of drying materials in a closed receptacle by subjecting them to heat under a sustained reduced pressure in the presence of a vapor maintained constantly saturated for an extended period of time and removing vapor from the receptacle during the dr ing operation.

3. The met 0d of drying materials in a closed receptacle by subjecting them to a sustained reduced pressure for an extended "period of time, continuously supplying heat to the materials by means of vapor generated in the receptacle, to vaporize the liquid.

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closed receptacle by subjecting them to heat under a sustained reduced pressure during thev entlre drying operation in the presence of a vapor maintained at a relativel high humidity for an extended period 0 time,

continuously supplying heat units by means of vapor to the said materials to offset the- 120 lowering temperature from the volatilizing of the liquid in the materials and removing the vapor from the receptacle during the drying'operation.

sure, constantly supplying and mainta ning 5. The method of drying materials containing water or other vaporizable sub-- a saturated vapor surrounding the material being driedto revent the material near-thesurface from rying' out first, vaporizing water or solvent, other than is contained in the material being dried, at a relatively low comprising in combination, a retort, anopen vaporizer of liquid in the retort, means for heating the retort to vaporize the liquid in the vaporizer and in the materials, and means for establishing and maintaining a reduced ressure in the retort and for removingtie formed vapors from the retort.

7. An apparatus for drying materials comprising in combination, a retort, means for heating the materials in the retort -to vaporize the liquid contained therein, means for constantly supplying and maintaining saturated vapor in contact with the said materials, and means for establishing and maintaining a reduced pressure in the retort and for removing the formed vapors from the retort.

8. An apparatus for drying materials comprising in combination a retort, means for constantly supplying saturated vapor to the retort, means-for maintaining a supply of heat to vaporize the liquid contained in the materials, and means; for establishing and maintaining a reduced. pressure in the retort and for removing the formed vapors from the retort.

9. An apparatus for drying materials comprising in combination, a retort, means for maintaining a supply ofheat to vaporize the liquid contained in the materials, means for constantly supplying saturated vapor to the retort and'comprising a body of water or other vaporizing solvent in communication with .the interior of said retort, means for vaporizing the said water or solvent, and means for establishing and maintaining reduced pressure in the retort and for removing the formed vapors from the retort.

10. An apparatus for drying materials comprising in combinationa retort, means for heating the materials in the retort and comprising a vaporizer, means for supplying heat to the vaporizer, the vaporcoming from the vaporizer serving as a heat carrying medium through the materials being dried, and means for establishing and maintaining a reduced pressure in the retort and for removing the formed vapors from the retort.

In testimony whereof I affix my signature.

JOSEPH P. DEVINE. 

